Designers of fuel systems for engines employed in boat and vehicle drag racing competition have been confronted with numerous vexatious problems not heretofore satisfactorily resolved. Currently, such engines are supercharged and utilise special and expensive fuels, such as nitromethane. Drag vehicle engines go substantially instantly from idle to full throttle operation and as quickly back to idle at race termination, whereas drag boat engines go from idle to a steady approach speed and then substantially instantly to full throttle and then instantly back to idle at race termination.
Heretofore, efforts to provide pressurized fuel injection systems meeting the exacting needs of such abrupt changes in engine operation involve many unsolved problems. For example, the fuel pumps used in such systems typically have a service life of only one to several races due to the severe operating conditions to which they are subjected. No satisfactory solution has been found for supplying sufficient fuel to provide the correct fuel/air ratio during the initial phase of acceleration, other than spring loaded check valves. The high pressure check valves employed for this purpose are the main cause of short pump life. Additionally no solution has been found for protecting the fuel pump from destructive high pressures developed upon abrupt closure of the fuel metering valve at race end.
Most prior proposals have endeavoured to use various arrangements of spring loaded check valves to control pressure in the fuel delivery ducting and/or in ducting venting excess fuel back to the fuel source. These proposals are subject to a variety of disadvantages including serious damage to components such as the fuel pump and the engine. My own efforts to solve these problems endeavoured to avoid spring biased check valves in the excess fuel venting ducting but were subject to the serious delay and tardiness in controlling excess fuel when initiating acceleration and particularly during deceleration. Smooth, rapid and highly efficient acceleration is dependent on substantially instantaneous cutoff of excess fuel and the immediate supply of 100% of engine acceleration fuel requirements. Likewise, it is critically essential to vent excess fuel substantially instantly upon release of the acceleration pedal at termination of the race as otherwise the resultant high increase in fuel pressure will seriously damage both the fuel pump and the engine. The present invention avoids these serious disadvantages using a metering valve having unique porting and operating characteristics.
The U.S. Pat. No. 3,473,523 to Hilborn recognises the presence of certain of the aforementioned problems and proposes techniques for resolving them. For example, he recognises the need for compensating for the delay in supplying adequate fuel during the initial phase of acceleration. To meet this need he provides normally closed check valves in the excess fuel return line. These valves are set to open in time delayed sequence at initiation of acceleration. This results in an excessively rich mixture, wastage of costly fuel, and in very rough, inefficient and harmful engine operation. He also attempts to protect the hot engine from the destructive effects of excessively rich fuel typically occuring during deceleration by providing a check valve controlled bypass for excess fuel set to open as his metering valve approaches its idle position. Unfortunately, the injector pump is often ruined by excessive fuel pressure rise inherently provided by this expedient.
Another serious shortcoming of fuel metering valves as heretofore proposed for drag engine fuel systems is the attempt to control fuel flow through one or more circular ports by a rotary valve member. It is not possible when using such valve structures to vary the fuel/air ratio in proportion to changes in engine speed from idle speed to instant throttle opening.